低密度奇偶校验码在EBPSK系统中的应用

Application of LDPC Code in EBPSK system

扩展的二元相移键控(EBPSK)是一种高效调制,为了降低其在低信噪比下的误码率,引入了低密度奇偶校验码(LDPC)。用BP算法对LDPC码进行译码时,需要计算译码初始信息。根据所用EBPSK解调器的特点,本文定义了解调输出的近似似然比,不仅可以降低系统的复杂性,同时通过仿真发现,利用其作为译码初始消息可以得到较高的信噪比增益。因此,在EBPSK系统中应用LDPC码以抵抗噪声、降低误码率是一种较有效的方式。

The Extended Binary Phase Shift Keying （EBPSK） is an effective modulation technique. In order to improve the BER performance under low SNR, the LDPC code is introduced. When using BP algorithm in LDPC decoding, the initial information needs calculating. According to the characteristic of EBPSK demodulator, the approximation likelihood ratio （LLR） of the demodulator outputs is defined in this paper. Simulation results show that it helps to reduce the complexity of systems, and obtain higher SNR gains with this approximation LLR as initial decoding message. Therefore, it is an effective method to adopt LDPC code to resist noise and reduce BER in EBPSK system.